1. Field of the Invention
The present invention relates generally to grooved friction materials, methods of making grooved friction materials and wet friction members using grooved friction materials. More particularly, the present invention relates to grooved friction materials formed of pyrolytic-carbon fabric material, methods for making same, and wet friction members using such grooved friction materials.
2. Description of the Related Art
In industrial and automobile clutches, brakes, automatic transmissions, limited slip differentials, hoists and similar friction power transmission and energy absorption devices, the devices typically include at least two cooperating members. Generally, at least one of the cooperating members is a support member and has a friction material surface adapted to be moved into and out of frictional engagement with an opposing surface on the other cooperating member. In liquid-cooled friction power transmission or energy absorption devices, both of the cooperating members typically move in a liquid, generally some type of cooling oil, and frequently the oil is force-circulating about and between the cooperating members so as to continuously lubricate or cool them. One friction material which has the desirable characteristics for such applications is a pyrolytic-carbon fabric material.
One such pyrolytic-carbon fabric material is disclosed in U.S. Pat. No. 4,291,794, which describes one way of forming the pyrolytic-carbon fabric material by densifying a single layer of woven cloth formed of carbon yarn strands. The densification step is performed by chemical vapor deposition of pyrolytic carbon onto the woven cloth. The densified woven cloth is then bonded onto the operating surface of one or more of the cooperating members. The surface of the densified woven cloth may then be grooved by machining or grinding. The grooves allow the cooling fluid to flow between the cooperating members in a manner which is optimum for a particular application.
The prior art has some serious shortcomings. To explain, one should understand that grooving of the densified woven cloth may be beneficial regarding clutching, braking, and/or accelerating for certain devices, especially those having large friction surfaces and/or those having to dissipate large amounts of heat. The grooves allow rapid clearing of cooling fluids, such as oil, from the friction interface. However, the process of machining or grinding the grooves into the friction surface of the woven cloth is a relatively costly procedure and, in addition, damages the yarn strands of the woven cloth because it removes a significant part of the individual yarns. This damage to the yarn strands weakens the woven cloth, especially at the edges between the grooves and the non-grooved portions of the woven cloth which can seriously impair the durability of the friction material. Furthermore, machined grooves result in rough surfaces which impair oil flow. This effect yields inferior cooling capacity and/or oil clearing capacity than is desired. As the grooves are helpful for heat extraction and lubrication, it is important to achieve this effect at an optimum rate.
Therefore, the present invention seeks to provide a molded grooved friction material formed of fabric material having minimally-damaged yarn strands on the friction surface so as to enhance its performance.
Another advantage being sought by the present invention is a wet friction member for friction engaging mechanisms, the wet friction member having a molded grooved friction surface formed of fabric material having minimally-damaged yarn strands to give the full strength of the friction material, while minimizing rough, machined grooves that impair oil flow to maximize heat extraction and lubrication.
Yet another advantage being sought by the present invention is a method for making a molded grooved friction material formed of a fabric material, the grooved friction material having minimally-damaged yarn strands on the friction surface.